Alice wants to send Bob a music file but keep it a secret from Eve. She encrypts the file in a certain way that Eve can't decrypt and sends it to Bob, who opens it and listens at his leisure.
The two problems with DRM are expressed as follows:
- In the typical DRM scenario, replace "Eve" with "Bob" to express the fact that the content is to be protected from the end users. The statement becomes an impossible dream.
- The other is a condition to add at the end: "After Bob has decrypted the file, he can only do with it what Alice decides to allow him". Bob has a decrypted file now, and there's nothing Alice can do about it.
Mokalus of Borg
PS - You could also destroy the user's equipment.
PPS - Or publish a sub-par media format and hope it catches on.